Deepawali or Diwali, the most pan-Indian of all Hindu festivals, is a festival of lights symbolising the victory of righteousness and the lifting of spiritual darkness. The word `Deepawali' literally means rows of diyas (clay lamps). This festival commemorates Lord Rama's return to his kingdom Ayodhya after completing his 14-year exile. Twinkling oil lamps or diyas light up every home and firework displays are common all across the country. The goddess Lakshmi (consort of Vishnu), who is the symbol of wealth and prosperity, is also worshipped on this day. This festive occasion also marks the beginning of the Hindu new year and Lord Ganesha, the elephant-headed god, the symbol of auspiciousness and wisdom, is also worshipped in most Hindu homes on this day. Details in http://www.hindufestivals.org
Another view is that Deepawali is meant to celebrate the destruction of the arrogant tyrant Bali at the hands of Vishnu when the latter appeared in his Vamana (dwarf) avatar. The occasion of Deepawali sees the spring-cleaning and white-washing of houses; decorative designs or rangolis are painted on floors and walls. New clothes are bought and family members and relatives gather together to offer prayers, distribute sweets and to light up their homes.
The Festival of Lights This is one of the oldest Hindu festivals occuring in the month of Kartik, which commemorates the return of Rama to Ayodhya after an exile of 14 years. It also marks the beginning of the new year and is celebrated with the lighting of lamps. Diwali or Deepawali, literally 'an array of lamps', is the festival of lights and is celebrated on the darkest night of Kartik. It is perhaps the most important festival in India. Originally a Hindu festival, it has now crossed the bounds of religion and is celebrated by all in India with fervor and gaiety. This day is a public holiday all over India. Diwali is also perhaps the oldest festival still celebrated today and is mentioned in the Ramayana. The celebrations include the lighting of lamps and candles, and the bursting of crackers (fireworks). Friends and neighbours exchange special sweets. People buy new clothes and in fact, in certain communities, it is absolutely essential to wear new clothes on this day. Diwali in India is equivalent to Christmas in the West. Therefore it is also the time when people get the festival bonus to their salaries. It marks the beginning of the new year for a large majority of Hindus, especially the trader community. Preparations for the festival begin many days prior to Diwali. It is time for a thorough cleaning of the house, for the belief is that Lakshmi will enter clean and nicely decorated houses. The scientific reason is that the monsoon is a time for insects and fungus to breed.With the end of the monsoon, homes need to be cleaned and painted, and belongings aired and dried before the onset of winter. The festival itself extends over about a week even though the most important day is the new moonday. In east Bihar and northern India, two days before Diwali is celebrated as Dhanteras in honour of Dhanvantari, the physician of the gods. He is believed to have emerged with a pot of amrita during the samudra manthan. People bathe early in the morning and observe a fast, which is broken only after sunset with sweetmeats, puri and other delicacies. On Dhanteras, new kitchen utensils are bought and kept at the place of worship. The buying of utensils, according to one theory, relates to the myth of Dhanvantari emerging from the ocean with a pot in his hand. Since he is also the physician of the gods, cleanliness and hygiene are essential to this festival. The day before Diwali is celebratedas Choti Diwali or 'small Diwali'. It is Diwali on a smaller scale, with fewer lights lit and fewer crackers burst. The morning after Choti Diwali, the women of the house make beautiful, coloured rangoli in the doorway and courtyard. Tiny footprints made out of rice paste are a special feature of the rangolis made for Diwali. They signify the footprints of Lakshmi, as she enters the house. In Hindu homes, Diwali celebrations involve a ritual puja to Lakshmi and also to Rama in the evening. Songs in honour of the gods are sung and arati is performed. Oil or ghee diyas are also lit. The gods are offered kheel, batashe and khilone and various sweetmeats. After the puja, the diyas are placed in and around the house: in the doorway, near the Tulasi plant, the backyard, every room and the back and front gates. After this, crackers are burst, and people meet friends and neighbours to exchange good wishes and sweets. Since Diwali falls on the new moon night, lamps are lit to brighten this moonless night. According to a myth, Lakshmi will not enter a dark house. The lamps also welcome home the spirits of dead ancestors, who are believed to visit on this auspicious night. In addition, the light frightens away any evil spirit that might be wandering about near the house on this night. In Orissa, lamps are lit to light up the dark path that the spirits of ancestors take back to heaven. In modern times, ghee diyas have been replaced by wax candles and coloured electric bulbs. In many areas, there is a competition of sorts among neighbours as everyone tries to have the brightest lights. The origin of Diwali can be traced back to ancient India, when it was probably an important harvesting season. It was thus extremely important to the largely pastoral Vaishya community. Their granaries were full, and the weather was good, at the end of the long monsoon and before the arduous winter. It was therefore a good time to celebrate. The Vaishya community began their new year with this happy occassion, after paying their debts and clearing their ledgers. As the religion developed, various mythological stories and explanations were attributedto this festival to give it religious sanction. However today, this historical explanation is all but lost among the many stories and folklore linked with the origin of the festival. According to the most popular one, Diwali is celebrated in honour of Rama, his consort Sita and brother Lakshmana, returning to their kingdom Ayodhya after a 14-year exile.To celebrate this event, people at Ayodhya are believed to have lit up their houses with lamps. The illuminations also symbolise the removal of spiritual darkness and the onset of happiness and prosperity. According to another belief, it is on this day that Lakshmi emerged from the ocean during the samudra manthan .Lakshmi Puja commemorates her birth and therefore forms a major part of Diwali celebrations. Being associated with the goddess of wealth and fortune, Diwali is specially important to the Vaishya community. Most tradesmen close their old ledgers and dealings and start afresh with new ledgers after Diwali. This day, with its emphasis on money, is also considered lucky for gambling. Giving social sanction to a vice, a popular saying states that one who does not gamble on this day will beborn a donkey in his next birth. Casinos and local gambling houses do brisk business during the Diwali week. In most homes, people invite their friends and relatives over to play cards. Another reason for the celebration of Diwali is that it marks the killing of the evil Narkasura at the hands of Krishna Naraka is believed to have abducted 16,000 women. Krishna killed him and rescued these women whom he later married. Naraka is the personification of hell and is believed to be the monsoon during which all activities come to a standstill. Though Diwali is equally important in the south and the north, the celebrations are markedly different. In South India, the story widely associated with Diwali is that of Narasimha, the man-lion incarnation of Vishnu. According to a legend, Hiranyakshipu was an evil demon king. He was unjust and cruel to his people. However, he was almost invincible, having extracted a boon from Brahma that he would be killed neither by beast nor man, neither inside nor outside, neither during the day nor at night. When his atrocities became unbearable, the gods sought Vishnu's help. Assuming his fifth incarnation of Narasimha, the man-lion,Vishnu killed Hiranyakshipu with his claws in the courtyard just before day break, hence steering clear of the boundaries of the boon. For this reason in the south, people light diyas in their houses on the day preceding Diwali. The next day begins early. First is the ritual bath, which begins with an oil massage of the hair and body. This is absolutely essential on this day. Its importance probably refers to cleaning oneself thoroughly after the monsoon months. After bathing, people receive new clothes and gifts from their elders, which they are expected to wear. The family then prays to Vishnu for its well-being and prosperity. After the prayers start the main celebrations which, as in the north, consist of bursting crackers and lighting candles.At day break, all celebrations end.People then visit friends and relatives and exchange sweets. References to the word 'atishbaji' or'crackers' are found even in ancient literature. The bursting of crackers is today the most important and eagerly-awaited part of the Diwali celebrations. According to one belief, the sound that resounds throughout the universe makes all aware of the great homecoming of Rama. Another belief is that the crackers are an indication ofthe joy of the people living on the earth, making the gods aware of their plentiful state. Still another possible reason has a more scientific basis: the fumes produced by the crackers kill a lot of insects, found in plenty after the rains. The use of high-tech bomb crackers is fairly recent. At times, Diwali celebrations get ugly, especially in the metropolitan cities. In New Delhi, people start bursting crackers in the evening and this continues till the early hours ofthe morning. As a result, the city is engulfed in toxic fumes and smoke for almost 10 hours. Another problem with crackers is that their manufacture is usually unregulated. As a result, the manufacturing units are unsafe and the material used is inflammable and toxic.Every year, many units are destroyed inaccidental fires, resulting in the death of those employed there. Kerala is probably the only state in India where even Hindus do not celebrate Diwali. The major festival there is Onam. In West Bengal, Kali Puja is performed on Diwali as it is believed that on this day Kali killed the wicked Raktavija. Being one of the main festivals of the trader community, markets are gaily decorated and lit up. Many safety measures and precautions are telecast on television and radio, especially for children. The fire departments are kept on the alert, and the municipal corporations of bigger cities also organise buckets and tankers of water at strategic locations. The second day after Diwali is celebrated as Bhai Duja when sisters apply tilak to their brothers and pray for their long and happy life. In all likelihood, this ritual was originally intended only for married women. Since they celebrated Diwali with their in-laws, this festival allowed them to come to their parents' home during this auspicious time. They got some time to meet the family and to rest after the hectic activity of the preceding week.And it gave their parents an opportunity to give them gifts, an opportunity they did not often get. Nowadays however, among many communities Bhai Duja is observed by both married and unmarried sisters. Details in http://www.hindufestivals.org